int IM_IMAGE_SIZEOF_ELEMENT( im )
int IM_IMAGE_SIZEOF_PEL( im )
int IM_IMAGE_SIZEOF_LINE( im )
int IM_IMAGE_N_ELEMENTS( im )
char *IM_IMAGE_ADDR( im, x, y )
IM_IMAGE_SIZEOF_ELEMENT(3) returns sizeof( one band element ).
IM_IMAGE_SIZEOF_PEL(3) returns sizeof( one pel ).
IM_IMAGE_SIZEOF_LINE(3) returns sizeof( one horizontal line of pels ).
IM_IMAGE_N_ELEMENTS(3) returns the number of band elements across a horizontal line.
IM_IMAGE_ADDR(3) returns a pointer to the pixel at position (x,y) in the image. The point (x,y) should lie within the image.
If the macro DEBUG has been defined, then IM_IMAGE_ADDR(3) will also perform bounds checking. If you ask for the address of a pel outside the image, then IM_IMAGE_ADDR(3) will print an error message of the form:
IM_IMAGE_ADDR: point out of bounds, file "test.c", line 18
(point x=50, y=0
should have been within Rect left=0, top=0, width=50, height=50)
and call abort(3).
DEBUG needs to be defined *before* vips.h is included. Either define DEBUG with -D in your Makefile, or have a #define DEBUG right at the top of your file.